Amplitude contractor and expander



May 2, 1939. H. sHoRE 2,156,658

` AMPLITUDE CONTRACTOR AND EXPANDER Filed May 19, 1934 500196Z: 0F .W6/WIS WAI/- HENRY SHORE ATTORNEY Patented May 2, i'.1939

PATENT oFFrcE AMPLITUDE CONTRACTOR AND EXPANDER Henry Shore, Elizabeth, N. J., assigner to Radio Corporation of America, a corporation of Dela- Ware Application May 19, 1934, Serial No. 726,433

4 Claims.

This invention relates to a method of and means for reducing the range of amplitudes of a transmitted signal and to a method of and Y means for expanding the amplitude range of the 5 signal after transmission back to its original value. In its broadest aspect the invention is based on the use of passive networks in conjunction with non-linear resistance. The non-linear resistance I make use of is a material known in the art and the character thereof in operation will be set forth in the description of my invention which follows.

In the prior art, where it has been desired to reduce the range of amplitudes of signal poten tials and then expand them back to their original value, tubes cooperating with complicated circuits and networks have been used. The arrangement an-d adjustment of the tubes and networks in these known systems is exceedingly critical with resultant high initial cost and high maintenance cost.

The object of my invention is to provide a new method of and means for reducing the amplitude range of signall potentials before transmission and expanding the amplitude range back to original value after transmission.

An additional object of my invention is to provide a new method of an-d means for reducing the range of amplitude of signalling potentials by means of a simple and inexpensive circuit for transmitting said potentials of reduced amplitude and a simple and inexpensive means for expanding the amplitudes of said signalling potentials back to their original value.

Briefly, the range in amplitudes of the signal potentials is reduced by applying said signal po# tentials to a simple' network in which a non-linear 'resistance is connected in parallel. The resistive value of the parallel resistance decreases faster 40` than linear with respect to the applied potentials.

In this manner the small amplitudes are increased and the higher amplitudes are reduced value. In the expander the non-linear resistance is placed in series in the network lso that it offers `high impedance to the low value potentials and offers a relatively low impedance to the high value potentials.

The novel features of my invention have been pointe-d out with particularity in the claims attached hereto. 'Ihe nature of my invention and the manner in which thesame is carried out will be better understood from the following description thereof and therefrom when read in connection with the attached drawing throughout which like reference characters indicate like parts insofar as possible and in which,

Figure l illustrates the essential elements of a signal voltage amplitude contractor,

Figure 2 shows the essential elements of a signal potential amplitude expander,

Figures 3 and 4 illustrate possible applications of the contractor and expander of the present invention; while,

Figure 5 is a curve illustrating the relation between the voltages applied to the terminals of the non-linear resistance used in my network and the current through said resistance and the value of said resistance.

Referring to the drawing, Figure l shows a contractor. The voltages to be reduced may be derive-d from any source and may be applied to the terminals l, 2 of the network. The network comprises a resistance R connected as shown and a non-linear resistance RX in shunt with the network. The terminals 3, 4 of the network may be connected with any repeating or utilization circuits but is preferably connected to the control grid of a thermionic tube which forms part of any repeater or amplifying or utilizing apparatus. In operation when a signal is placed on the terminals l, 2 of the network as the amplitude of the signal rises the resistance of RX decreases at a rate greater than linear. Consequently the voltageacross the terminals 3, is reduced relative to -the input voltage since the rapid decrease of the resistance of RX produces a disproportional current through the resistance R., increasing the voltage drop across R to a greater extent than -would occur without Rx. Consequently signals of large values are reduced in amplitude while signals of low value are increased in amplitude. The latter is because the signals of low amplitude had little or no effect on the linearity of Rx and consequently produce a small drop through R. For example, if the original signal range is 40' decibels, my contractor would reduce its range to say 2O decibels'. n The relation between the signal voltages applied to RX and the resistance thereof and the current therethrough is illustrated in Figure 5. In Figure 5, Which merely serves-to illustrate what takes place in Rx when signal potentials are applied thereto, i is the current. It is noted the current through Rx increases at a rate faster than linear with respect to the applied voltage plotted as abscissa. Conversely the resistance r of RX decreases at a rate greater than linear with respect to the applied voltage.

In the expander as illustrated in Figure 2 the non-linear resistance Rx is connected in series with one of the lines as shown. The line is shunted by a linear resistance Rp as shown. The terminals of the line 1, 8 here, as in the prior figure, may be connected to any utilization or repeating apparatus or amplifying apparatus and is preferably connected to the control grid and cathode of a tube included in said apparatus. For the low values of signal potentials applied to the terminals 5, 6 the non-linear resistance Rx exhibits very high resistive value so that the voltage available at the terminals 1, 8 of the network is very small. As the signal increases a greater percentage of input voltage becomes available at the terminals 1, B of the network .due to the greater than linear decrease of the resistive value of RX. Consequently signals of large value have their amplitudes increased above what they would be in the case of a linear series resistance in place of Rx, while signals of low value are reduced a greater amount than they would be if a linear resistance were used in place of Rx. Thus if a signal potential of a range of 20 decib-els is applied to the terminals 5, 6 of the expander, the output range at 1, 8 would be 40 decibels.

Obviously the present invention is of wide application in the radio art. For example in many cases it is desired that the signals be maintained Within a predetermined amplitude range for transmission. In this case the amplitudes of the signals may be contracted by means of my simplified method and network before transmission and expanded back to their original values after transmission. This is of considerable value in transmitting speech or other amplitude modulated signals over a radio path or any other transmission medium where there is noise present, since by decreasing the range of amplitude variation a much better signal to noise ratio can be obtained.

In Figure 3 I have shown an application of the contractor and expander of the present invention. I-Iere it is assumed that the signals are to be transmitted over a. transmission medium efiiciently permeable to a known amplitude range. Signals from any source of signals Hl are applied to a network including a resistance R and a non-linear resistance Rx connected as shown to the input electrodes of a thermionic repeater I2. The amplitude range of the signals is contracted in the network and the signals of altered relative amplitudes are applied by way of transformer I4 to the transmission medium. The transmission medium may be simple lines or may7 include as shown necessary amplifiers. The terminal of the transmission medium is connected as shown to a second network including a nonlinear resistance RX. The network including the resistance Rx is connected to the input electrodes of a thermionic repeater amplifier I8. A linear grid resistance Rp is connected across the lines 1 and 8. This network returns the signal amplitudes to their original relative values, applies the corrected amplitudes to the input electrodes of f repeater i8, so that undistorted signals similar to the signals source l are applied on the utilization apparatus. The effect of the contractor network on the signal potentials is complementary to the effect of the expander network on the signal potentials.

Of course my invention contemplates the use ofv the contractor and expander in radio frequency work and is applicable to signal potentials alone or when impressed on carrier waves. For example, as shown in Figure 4, the signal range may be contracted and the signals of reduced range may be impressed on a modulator 20 wherein they are used to modulate carrier waves from a source 22. The modulated carrier may be radiated after further amplification and/or frequency multiplication where desired. At the receiver the radiated wave may be demodulated by means of a tuned radio frequency device or by means of a demodulatcr of the heterodyne type and the demodulated signals may be impressed on a signal range expander which may be in turn connected with a thermionic tube I8, so that the signals are returned to their normal relative amplitudes in the utilization apparatus.

Having thus described my invention and the operation thereof, what I claim is:

1. A signaling system for varying the amplitude of signal potentials comprising a source of signal input potential, a network including a linear passive resistance and a non-linear passive resistance both of which have one terminal directly connected to the input grid of a thermionic repeater, a transformer coupled to the output electrode of said thermionic repeater, an amplifier connected to said transformer, said amplifier connected to a transmission medium, a utilization circuit, a second network including a non-linear passive resistance and a linear passive resistance both of which have one terminal directly connected to the input grid of a thermionic repeater, the non-linear passive resistance in both the first and second networks being traversed solely by a signal frequency current due to the signal potential applied to said grid so that the controlling effect results solely therefrom, and character of said last mentioned non-linear passive resistance network being complementary to the character of said first mentioned resistance network, said second repeater network having its input coupled to the output of said rst circuit and its output coupled to the input of said utilization circuit.

2. A signaling system for varying the amplitude of signal potentials comprising a source of signal input potential, a network including a linear passive resistance directly connected in series with the input grid of a thermionic repeater, a non-linear passive resistance directly connected in shunt with said input grid of the thermionic repeater and the source of signal input potential, a transformer coupled to the output electrode of said thermionic repeater, an amplifier connected to said transformer, said amplifier connected to a transmission medium, a utilization circuit, a second network including a non-linear passive resistance and a linear passive resistance both of which have one terminal directly connected to the input grid of a thermionic repeater, the non-linear passive resistance in both the first and second networks being traversed solely by a signal frequency current due to the signal potential applied to said grid so that the controlling effect results solely therefrom, the character of said last-mentioned non-linear passive resistance network being complementary to the character of said first mentioned resistance network, said second repeater network having its input coupled to the output of said first circuit and its output coupled to the input of said utilization circuit.

3. A. signaling system for varying the amplitude of signal potentials comprising a source of signal input potential, a network including a linear passive resistance and a non-linear passive resistance both of which have one terminal directly connected to the input grid of a thermionic repeater, a transformer coupled to the output electrode of said thermionic repeater, a modulation amplier coupled to said transformer, said modulation amplier being connected to a transmission medium, signal receiving means including a utilization circuit, signal absorbing means, and a signal demodulating means, a second networkincluding a non-linear passive resist-ance and a linear passive resistance both of which have one terminal directly connected to the input grid of a thermionic. repeater, the non-linear passive 'resistance in both the first and second networks being traversed solely by a signal frequency current due to the signal potential applied to said grid so that the controlling e'ect results solely therefrom, the character of said last mentioned network being complementary to the character of said first mentioned resistance network, said second repeater network having its input coupled to the output of said first circuit and its output coupled to the input of said utilization circuit.

4. A signaling system for varyingl the amplitude of signal potentials comprising a source of signal input potential, a network including a linear passive resistance directly connected in series with the input grid of a thermionic repeater. a.

non-linear passive resistance directly connected in shunt with said input grid of the thermionic repeater and the source of signal input potential, a transformer coupled to the output electrode of said thermionic repeater, a modulation amplifier connected to said transformer, said amplier being connected to a transmission medium, a utilization circuit, signal absorbing means, and a signal demodulating means, a second network including a non-linear passive resistance and a linear passive resistance both of which have one terminal directly connected to the input grid of a thermionic repeater, the non-linear passive resistance in both the first and second networks being traversed solely by a signal frequency current due to the signal potential applied to said grid so that the controllingeifect results solely therefrom, the character of said last mentioned non-linear passive resistance network being complementary to the character of said rst mentioned resistance network, said second circuit repeater network having its input coupled to the output of said rst circuit and its output coupled to the input of said utilization circuit.

HENRY SHORE. 

